51 % Attack in Blockchain is an attack where the single entity controls more that 51% of Hashing power in blockchain network. When a single body has more that 51% of hashing power , they can prevent transaction from gaining the confirmation and prevent other miners in completing new block. Similarly, they can also reverse the transaction often called as double spending coin. For example : If you send the 1 BTC to another user, they can reverse transaction is such a way that both party have 1 BTC. However , changing past record of blockchain transaction becomes difficult in bitcoin.
Is there any chance that there will be any 51% attack?
During past years, it has been recorded that some blockchain network like Ethereum Classic had a 51% Attack. There is chance that blockchain network can undergo 51% attack. However, controlling huge blockchain network like Bitcoin become extremely difficult as it is difficult to control the 51% of bitcoin network's hashing power.
So, There is a possibility of 51% attack in future. However, meeting such a requirements becomes extremely difficult as it requires a lot of hashing power. When the blockchain network is very small, we must consider 51% attack is huge threat at there is chance of controlling the network through 51% attack. And there is less possibility of 51% attack in larger blockchain network like of Bitcoin as Controlling the network become extremely difficult.
